A magnet arrangement for detecting the angle of rotation of a mechanical shaft is known, for example, from the patent U.S. Pat. No. 4,810,967. In this case, the magnet arrangement comprises a magnetic ring which is slipped onto a shaft. The magnetic ring is provided with a magnetic coding around its periphery which is read by at least one magnetic field sensor. Because the magnetic ring with its magnetic coding is slipped onto the shaft, it makes the cylinder jacket surface of the shaft appear bigger and effects a considerable increase in the local diameter of the component comprised of shaft and magnetic ring at the location of the magnetic ring. Such a shaft can only be fitted into arrangements in which there is a sufficiently large space available to house the additional magnetic ring.
A further disadvantage of a shaft with a magnet arrangement such as in U.S. Pat. No. 4,810,967 lies in the expensive coding of the magnetic ring around the periphery. In this case, the attainable angular resolution depends upon the fineness of the coding and the number of individual magnetized zones. The greater the number of magnetized zones, the greater the angular resolution. However, a large number of magnetized zones means that the ring has a large circumference with the previously mentioned design disadvantages. Apart from that, such magnetic scale codings require a great deal of time and money.
A further disadvantage of mechanical shafts with scale codings attached to their cylinder jacket surfaces is that the cylinder jacket surface can no longer transmit any power at the location of the scale coding. This means a substantial design limitation if, for example, the cylinder jacket surface of the shaft is to be equipped with a gear for power transmission.
The object of the invention is therefore to propose a mechanical shaft with an integrated magnet arrangement which, together with a magnetic field sensor, enables the angle of rotation position of the shaft to be detected. In so doing, the magnet arrangement should not require any additional structural space in order to fit the mechanical shaft into an arrangement and its design should be kept as simple as possible.
In accordance with the invention, this task is solved by the features of the independent claim. Further advantageous embodiments are contained in the subclaims.
The solution is achieved by fitting a permanent magnet, a non-magnetic screening and at least two pole shoes into a recess in the face of the shaft end. The magnetic field of the permanent magnet is shaped by a non-magnetic screening and by a special arrangement of additional pole shoes. The non-magnetic screening encloses the permanent magnet and the pole shoes like a box with four side walls and a bottom plate, and screens the magnetic field of the permanent magnet from the material of the mechanical shaft. If the material of the mechanical shaft is made of a non-magnetic material then there is no need for additional screening. In this case, the magnet arrangement of permanent magnet and pole shoes is fitted directly into the recess in the face of the shaft. Together with the oblong permanent magnet, the pole shoes form a U-shaped arrangement, in which the pole shoes form the two legs of this U-shaped arrangement and the linear permanent magnet the connecting yoke. In this way, a uniformly homogeneous magnetic field is created between the two free legs of the pole shoes with very good parallel alignment of the field lines. A direction-sensitive magnetic field sensor securely fitted between the free legs of the pole shoes produces, in the case of a rotational movement of the mechanical shaft and the thereby inevitably linked change in the direction of the magnetic field between the legs of the pole shoes, a sinusoidal signal whose value is a measure for the angle of rotation of the shaft corresponding to the trigonometrical functions.
The following principal advantages are achieved through the invention:
The mechanical shaft with an integrated magnet arrangement according to the invention makes a mechanical shaft available whose angle of rotation can be detected without contact. The mechanical shaft according to the invention can be particularly advantageously used where there is no structural space available for an additional measuring arrangement outside the shaft. This makes the mechanical shaft according to the invention particularly suitable as, for example, a component of the rotor of an electric motor or as a component of a toothed wheel gear. Conventional magnetic scale arrangements on the cylinder jacket surface of a drive shaft would normally require a free cylinder jacket surface here, so that the shaft would have to be lengthened to accommodate the scale arrangement in comparison to a drive shaft without scale arrangements.
The design of the magnet arrangement for the mechanical shaft according to the invention can be kept very simple and very small. This also enables the recess for accommodating the magnet arrangement to be kept very small. This is particularly advantageous if the magnet arrangement is recessed into the faces of drive shafts. As a rule, the recess can be kept small in comparison to the dimensions of a drive shaft of a toothed wheel drive or a powerful electric motor, so that the structural mechanical strength properties of the drive shaft are hardly affected by the recess.